Question

Which option describes the characteristics of magnetic field produced by current in a long,straight wire ?

• A. The field is uniform.
• B. The field increases in strength as the distance from the wire increases.
• C. The field lines are directed parallel to the wire, but opposite to the direction of the current.
• D. The field lines are directed radially outward from the wire.
• E. The field lines form circles about the wire.

Answer 1

The correct option is E The field lines form circles about the wire.

The magnetic field at distance r from wire is $B=\frac{{\mu }_{0}I}{2\pi r}$

Thus, the field decreases in strength as the distance from the wire increases.
The direction of the magnetic field is in the direction the fingers of your right hand would curl if you wrapped them around the wire with your thumb in the direction of the current. Thus, the filed lines will form circles about the wire.